Definition of macro and micronutrients
Macronutrients and micronutrients are the essential mineral elements that are required for a plant to grow and complete its lifecycle. The prefixes “macro” and “micro” are used to describe the quantity necessary for optimal growth, with “macro” meaning larger and “micro” meaning smaller. So, when you hear the terms essential macro- or micronutrients, think plant nutrition for optimal health and growth.
Nutrient uptake and mineral deficiencies in plants
In contemplating plant nutrition, there is one word that should also always be kept in mind: synergy. In discussing macronutrients and micronutrients, it is imperative to remember that no one nutrient, despite the amount required for optimal growth, is more or less essential and that, despite common simplistic prescriptive advice of adding one or two nutrients, plant health is determined by a complex and synergistic relationship between all nutrients and microorganisms in a soil.
Other factors, such as soil PH, can also influence the bioavailability of certain nutrients, so it is always best to have a soil tested before applying any sort of fertilizer or nutrient. Only a soil test will reveal what needs to be amended in order to achieve optimal nutrient ratios for plant health and growth. The University of Guelph is a great option for information and soil testing.
So, with synergy in mind, let’s learn about the nutrients that are essential for plant health.
Macronutrients in soil
Plants require nitrogen to form amino acids, the building blocks of proteins. Proteins are essential for life and perform numerous functions within a plant. Proteins are responsible for synthesizing DNA, the genetic material or instructions necessary for a plant to live and grow; proteins also provide structural support in cell walls and are integral in nutrient transport and enzymatic reactions. Plants that are yellowing, stunted or slow-growing may be deficient in nitrogen.
In terms of plant health, phosphorus is critical for photosynthesis and growth. If you find your plants are slow-growing or notice the foliage changing from a vibrant green to purplish-red or blue, a phosphorus deficiency may be the problem.
Potassium helps to regulate turgor pressure (i.e., allows a plant to maintain its structure) as well as numerous other essential enzymatic reactions. If you find your plant leaves are looking scorched or dry and brown at the leaf tips and edges, supplementing the soil with a potassium source may help.
Sulphur is essential in the formation of certain amino acids. It is also necessary for the formation of numerous enzymes and plant chlorophyll. Pale green leaves (i.e., especially new growth) may indicate a sulphur deficiency.
Magnesium is necessary for the formation of chlorophyll, for enzymatic activity and for the utilization of carbohydrates and fats. A deficiency in magnesium may present as foliage drooping and chlorosis, a yellowing of leaves and veins.
Calcium is necessary for nutrient transport, structural support, enzymatic activity, and cell division. Once deposited into plant tissue, it is non-translocatable, so a steady supply of calcium from the soil is necessary for plant health and growth. In certain species of plants, calcium is necessary in order to utilize nitrogen and other essential nutrients. A deficiency in calcium can present as stunted or abnormal growth, black spots on leaves and chlorotic leaf veins.
Micronutrients in soil
Iron acts as a catalyst for the formation of chlorophyll. It is also involved in numerous enzymatic reactions. A deficiency may present as chlorosis and stunted growth.
Manganese is necessary for photosynthesis, respiration and the utilization of nitrogen. A deficiency of manganese may present as chlorosis, with leaves eventually turning white and falling off. There may also be spotting (i.e., grey, brown or blackish) on leaf veins.
Boron is involved in numerous plant functions and, like calcium, is non-translocatable. Thus, a steady supply of boron must be present in the soil for optimal growth. Boron is necessary for structural support, hormonal activity, nutrient transport, calcium utilization and flowering. A deficiency may present as a lack of terminal buds and flowering. A deficiency may also cause leaves to become crumbly, thick and curled.
Zinc is necessary for enzyme formation and for numerous enzymatic reactions. It is essential for hormonal activity, the formation of proteins and the utilization of carbohydrates. A deficiency in zinc may lead to an iron deficiency. Symptoms of a zinc deficiency may present as spotted and chlorotic leaves.
Copper is essential for nitrogen metabolism and is, thus, usually found near root systems. It is also an integral component of certain enzymes and enzymatic activities. A deficiency may present with a shrivelling back of shoot tips and brown spotted leaves.
Molybdenum is necessary for the utilization of nitrogen and, thus, protein formulation. It is a component of an enzyme that renders soil nitrogen usable or bioavailable to plants. It is also required by nitrogen-fixing bacteria on root nodules. Plants deficient in molybdenum may simply stop growing and present as chlorotic with curled leaves.
Chlorine is necessary for photosynthesis and involved in osmosis and maintaining the ionic balance necessary for mineral utilization. A deficiency may present as chlorosis, stunted or shortened roots, wilting, bronzing and reduced fragrance.
Nickel is necessary for the utilization of nitrogen and the absorption of iron. It is also essential for seed health and germination. A nickel deficiency is usually noticeable at the time of reproductive growth and may affect seed health and overall plant fertility.
Sodium, like chlorine, is involved in osmosis, the water movement throughout the plant, and in maintaining the ionic balance necessary for proper mineral utilization.
Beneficial micronutrients for plants
Cobalt is essential for nitrogen utilization in legumes and for nitrogen-fixing bacteria on the root nodules of non-legume plants. A cobalt deficiency may present with the symptoms of a nitrogen deficiency: chlorosis and stunted or slowed growth.